A method of enhancing performance of a combustion engine involves using a hydrogen generator to generate HHO. When HHO is mixed with the air-fuel mixture, the fuel burns cleaner and more torque is generated. However, should the engine backfire, there is a danger that hydrogen gas which has ignited by the backfiring engine will proceed backwards through the hydrogen generator. The resulting explosion can potentially damage the vehicle and injure any occupants. U.S. Pat. No. 5,531,199 (Bryant et al) discloses the use of a blow-back valve to address this concern. There will hereinafter be described an alternative method and associated apparatus for addressing blow-back.